1. Field of the Invention
The present invention relates to a film formation method and film formation apparatus for forming an insulating film on the surface of a substrate to be processed, by generating a plasma in a processing chamber and at the same time introducing a film formation gas into the processing chamber.
2. Related Background Art
A high-density plasma (HDP) type CVD apparatus is available as one film formation apparatus. When a film is to be formed on a semiconductor substrate by using this HDP type CVD apparatus, the semiconductor substrate is first supported on a support member in a processing chamber. Source RF power is then applied to a coil antenna installed in the processing chamber to generate an inductively coupled RF plasma (ICP) in the processing chamber. In addition, a film formation gas is introduced into the processing chamber. Bias RF power is applied to the support member to allow the plasma species generated in the processing chamber permeate the substrate surface. In this manner, an insulating film such as SiO2 is formed on the substrate.
Recently, as the thickness of a gate oxide film of a MOS transistor decreases to 10 nm or less, this gate oxide film is often destroyed by charge-up in a semiconductor manufacturing apparatus using a plasma. The conventional method of reducing this plasma damage to the gate oxide film is to reduce the potential of a plasma, uniformize a plasma, or control the amount of electric charge injected into a wafer as in an ion implantation apparatus. These techniques are very effective in an etching apparatus and an ion implantation apparatus. However, these countermeasures are still unsatisfactory in an apparatus which forms an insulating film on the surface of a substrate, such as an HDP type CVD apparatus described above.
It is an object of the present invention to provide a film formation method and film formation apparatus capable of reducing plasma damage to a substrate to be processed.
The present inventors made extensive studies and have found the following. That is, when at the end of film formation the introduction of a film formation gas into a processing chamber is stopped while bias RF power is applied to a support member, the plasma density above a substrate to be processed becomes nonuniform owing to the influence of the film formation gas remaining in a pipe. If the application of the bias RF power to the support member is stopped in this state, plasma damage to the substrate readily occurs. On the basis of this finding, the present inventors have completed the present invention.
That is, the present invention is a film formation method of forming an insulating film on the surface of a substrate to be processed supported on a support member in a processing chamber, characterized by comprising the steps of forming a film on the substrate, while a plasma is generated in the processing chamber and a film formation gas is introduced into the processing chamber, by making the plasma permeate the substrate by applying bias RF power to the support member, and stopping the application of the bias RF power to the support member while the film formation gas is kept introduced into the processing chamber, and completing the film formation on the substrate by stopping the introduction of the film formation gas after that.
In the present invention as described above, during the film formation process in which the film formation gas is kept introduced into the processing chamber, the supply flow rate of the film formation gas is so set that the film thickness of an insulating film formed on the surface of a substrate to be processed becomes substantially uniform. Accordingly, the plasma density above the substrate is substantially uniform, and the plasma in this state permeates the surface of the substrate. Therefore, even when the application of the bias RF power is stopped while the film formation gas is kept introduced into the processing chamber, the electric charge balance on the surface of the substrate is maintained in a relatively good condition. This can reduce plasma damage to the substrate.
Preferably, when the film formation gas is introduced into the processing chamber, the film formation gas is supplied toward the surface of the substrate from the upper portion and side portion of the support member. Accordingly, substantially equal amounts of the film formation gas can be supplied to the center and edge of the substrate. This makes it possible to further improve the uniformity of the film thickness of the insulating film formed on the substrate. Consequently, plasma damage to the substrate can be further reduced.
Preferably, a gas containing a silicon-containing gas and an oxidizing gas is used as the film formation gas. In this case, an SiO2 film can be formed as an insulating film on the surface of the substrate.
Preferably, after the application of the bias RF power to the support member is stopped, the introduction of the silicon-containing gas into the processing chamber is stopped, and subsequently the introduction of the oxidizing gas into the processing chamber is stopped. By sequentially stopping the introduction of gases in this manner, the occurrence of nonuniform plasma distribution can be minimized.
For example, SiH4 gas is used as the silicon-containing gas, and O2 gas is used as the oxidizing gas.
Also, the present invention is a film formation apparatus for forming an insulating film on the surface of a substrate to be processed supported on a support member in a processing chamber, characterized by comprising plasma generating means for generating a plasma in the processing chamber, plasma permeation means for making the plasma generated by the plasma generating means permeate the substrate by applying bias RF power to the support member, gas introducing means for introducing the film formation gas into the processing chamber, and control means for controlling the plasma permeation means for stopping the application of the bias RF power to the support member while the film formation gas is kept introduced into the processing chamber, and controlling the gas introducing means for stopping the introduction of the film formation gas after that.
The above-mentioned film formation method can be practiced by thus using the plasma generating means, plasma permeation means, gas introducing means, and control means. Accordingly, plasma damage to the substrate to be processed can be reduced.
Preferably, the gas introducing means comprises a first nozzle formed in the upper portion of the processing chamber to spray the film formation gas toward the surface of the substrate, and a plurality of second nozzles formed in the side portion of the processing chamber to spray the film formation gas toward the surface of the substrate. With this construction, substantially equal amounts of the film formation gas can be supplied to the center and edge of the substrate. Therefore, the film thickness of the insulating film on the substrate becomes more uniform. As a consequence, plasma damage to the substrate can be further reduced.
Preferably, the gas introducing means comprises a silicon-containing gas introduction system for introducing a silicon-containing gas into the processing chamber, and an oxidizing gas introduction system for introducing an oxidizing gas into the processing chamber. In this case, a gas containing the silicon-containing gas and the oxidizing gas is introduced as a film formation gas into the processing chamber.
Preferably, the control means controls the plasma permeation means to stop the application of the bias RF power to the support member, controls the silicon-containing gas introduction system to stop the introduction of the silicon-containing gas into the processing chamber, and then controls the oxidizing gas introduction system to stop the introduction of the oxidizing gas into the processing chamber.
Preferably, the processing chamber comprises a chamber main body in which the support member is placed, and a lid made of an insulating material and mounted in the upper portion of the chamber main body, a coil being attached to the outer surface of the lid, and the plasma generating means generates a plasma in the processing chamber by applying source RF power to the coil. Thus, a plasma can be effectively generated in the processing chamber.